The present invention relates to engine/transaxle combinations used as driving means for working vehicles.
FIG. 2 shows a conventional working vehicle 10 equipped for lawn mowing. The conventional work vehicle 10 includes a steering wheel 11, an operator's seat 13 and a mower deck 16 or other working implement which is conventionally operatively connected to the vehicle through two traction bars 17, 18. A drive unit 20 which includes an engine 21 is positioned between the two front wheels 22 and/or two rear wheels 24. As shown, a conventional transaxle 26 is positioned on the mower deck 16 side of the rear wheels 24. Driving power is provided from the engine 21 to the mower deck 16. A V-belt system 28 is operatively positioned between the engine 21 and the mower deck 16 for transmitting power from the engine 21 to the mower deck 16 or other implement.
In the central portion 30 of the transaxle, a speed reduction unit and a differential unit (not shown) are operatively positioned in close proximity to each other, as shown in Japanese Patent unexamined publication No. 56-23065. In the conventional structure, a first V-belt 32 is provided for transmitting power between a belt pulley 33 operatively connected to the output end of the engine crankshaft 34 and a second belt pulley 36 operatively connected to an intermediate shaft 38 which is conventionally connected to the transaxle 26. A second V-belt 40 is provided for transmitting power between a third belt pulley 41 operatively connected to the intermediate shaft 28 and a fourth belt pulley 42 operatively connected to the input shaft 43 of the mower deck 16 or working implement.
With the conventional vehicles, the intermediate shaft 38 having the second 36 and third 41 pulleys is required because the relative thickness of the central portion 30 of the conventional transaxle prevents the moWer deck 16 Or other attached implements from having sufficient operational vertical movement or float relative to the work vehicle. Therefore, utilizing a single V-belt between the engine output shaft 34 and the input shaft 43 of the work implement to transmit power is not practical because the conventional intermediate shaft 38 with pulleys provides the ability for the V-belt connecting the intermediate shaft and the implement to float vertically in response to convex or concave conditions in the operating surface without interference between the belt and the conventional thick transaxle housing. Specifically, as shown, with the intermediate shaft 38, if the mower deck 16 is moved vertically, the second V-belt 40 will move vertically, but the first V-belt 32 will not move vertically. Therefore, with this conventional construction, the central thick portion 30 of the transaxle is prevented from contacting or interfering with the first V-belt 32.
However, in the above described conventional structure the distance between the intermediate shaft 38 and the implement input shaft 43 is relatively short and the second V-belt 40 will reach its maximum acceptable belt misalignment angle (+/- 5.degree.-8.degree.) for extended operations with rather limited vertical movement of the mower deck 16 when compared to the vertical movement possible by utilizing a longer belt. Thus, because of the conventional transaxle structure, two belts and an intermediate shaft and pulleys are required resulting in increased cost and complexity, not to mention the restricted vertical float. Further the conventional two belt system is apparently subjected to increased bending frequency thereby resulting in reduced service lives for the V-belts.
In order to increase the actual vertical float distance, it appears necessary to increase the distance from the engine output shaft pulley to the implement input shaft pulley in order to increase the distance above and below the normal level implement position which the implement can float. This is due to the acceptable belt misalignment angle mentioned above. Specifically, as the distance between the engine output crankshaft pulley and the implement input pulley decreases, the smaller the distance above and below the normal level implement position the implement can float without exceeding the belt misalignment angle. Because with the conventional pulley and belt system utilized to transmit power from the engine output crankshaft to the implement input shaft having two pulleys and an intermediate shaft, the conventional system is restricted relative to the belt's misalignment angle above and below the implement level plane. In other words, the shorter the distance of any one belt, the less the distance the implement can deviate from both above and below the level implement position without exceeding the belt misalignment angle.
With the conventional structure, the intermediate shaft is required partially because the engine crankshaft and the transaxle centerline have been separated by such a relatively great distance. Therefore, utilization of one belt for transmitting power from the engine output shaft to the implement input shaft was impractical. Specifically, even if there were sufficient clearance between a single belt and a lower portion of the transaxle housing to enable the belt to pass thereunder and to allow some vertical float, since the distance separating the engine crankshaft and the transaxle housing was relatively great, the vertical float angle provided at the engine crankshaft pulley was less in the vertical direction than the belt misalignment angle due to interference between the belt and the bottom portion of the transaxle.
An additional problem encountered with conventional engine transaxle arrangements during the development of the present invention involved how you assemble the engine and transaxle into a unit while maintaining an acceptable vehicle center of gravity simultaneously with an acceptable clearance between the bottom of the engine output shaft and the ground. With the engine and the conventional transaxle configured as a unit, the vehicle center of gravity was too high for use in front mount mower-type vehicles and the conventional hydrostatic transaxle drive arrangement whereby the hydropump was conventionally driven by the engine crankshaft provided inadequate ground clearance for the engine crankshaft.
With conventional engine transaxle configurations, having hydrostatic transmissions, separate lubricating systems have been used to separately lubricate the engine, the differential and to provide hydraulic fluid for the hydrostatic transmission. If the hydrostatic fluid system and the engine lubricating fluid system along with the transaxle system could be interconnected, a simpler, more serviceable unit would result.
Accordingly, there is a need for an improved engine transaxle combination which eliminates the intermediate shaft and the two pulleys; which provides adequate clearance so that a single V-belt can be connected directly between the engine output shaft and the mower deck or other working implement input shaft; which positions the engine relatively close to the transaxle center line thereby decreasing the distance from the engine output shaft to the implement input shaft while simultaneously maintaining an acceptable vehicle center of gravity; which shortens the engine output shaft so that adequate ground clearance is maintained; which utilizes the engine crankshaft to drive the hydropump from a location inside the engine; which eliminates interference between the single V-belt and the transaxle housing; which provides for increased vertical implement float; which provides for reduced cost in both material and assembly labor; which simplifies the connection between the engine output shaft and the mower deck or other working implement; which provides for common fluid between the engine and at least one other of the hydrostatic transmission, the differential, and/or the axle.